Hot melt material application devices incorporating slot-type dies are known. Such devices are typically used to continuously apply a coating to a substrate which passes over a coating surface of the die head. Designs for such slot dies must insure that (i) the hot melt material is evenly redistributed from the surface of the die head to the surface of the substrate being coated and (ii) the configuration of the doctoring, or finishing, surface of the die head is carefully controlled.
Controlled redistribution of the hot melt material from the die head surface to the substrate surface is typically accomplished by means of the design of the internal flow passages of the die. Generally, two types of internal flow passage designs are known. The so-called coat hanger dies (e.g. U.S. Pat. No. 4,687,137, assigned to the assignee of the present invention) utilize complex internal machined surfaces which permit the hot melt material to flow from the die head to the substrate in a uniform manner. However, utilizing this type of arrangement generally limits the applications of the die to a limited number of coating widths, and to certain ranges of hot melt material flow and viscosity.
T-slot dies have also experienced widespread use in the industry (see e.g. U.S. Pat. No. 5,294,258, also assigned to the assignee of the present invention). Typically these types of dies can accept a wider range of hot melt material types than coat hanger dies. In addition, T-slot dies may be used for applying varying amounts of hot melt material by merely by changing shim plates on the device. However, known T-slot dies are not as efficient as coat hanger dies in evenly internally distributing the hot melt material from within the die head to the doctoring surface.
Moreover, both known T-slot and known coat hanger dies provide limited control over the configuration of the doctoring surface of the die head to accommodate for variations in the doctoring surface of the die or the surface of the back up roll, or cross-machine variations in the thickness of the substrate being coated. To insure consistent distribution of the hot melt material across the substrate, means for adjusting the configuration of the doctoring surface must be provided. These adjustment means must be durable and wear-resistant in order to be repeatedly operable with precision over the life of the die.
Accordingly, it is an object of the present invention to provide a die having a head which provides both the even internal flow distribution of a coat hanger die and the flexibility of application and coating width variation a T-slot die. It is an additional object of the invention to provide such a die which will accommodate variations in the doctoring surface of the die, the surface of the back up roll, and the thickness of the substrate.